This invention relates to all forms of chromatography, e.g., liquid, gas-liquid and gas-solid, which use separation columns having at least their active surfaces made of glass or other siliceous material. The invention also relates to methods for preparing the separation columns, which include capillary (open) columns and support-coated open tubular (SCOT) columns as well as packed columns of all sorts. (As employed throughout the following description and claims, the expression "active surfaces" refers to those surfaces of the column, including the packing material in the case of packed columns, which carry the stationary phase effecting the chromatographic separation or partitioning process.) For additional information as to both capillary (sometimes referred to as open tubular or Golay) columns, as well as to SCOT and packed columns, reference may be had to respective U.S. Pat. Nos. 2,290,478 to Marcel J. E. Golay; and 3,295,296 and 3,340,085 to I. Halasz and C. Horvath.
Glass has often been considered as a preferred material for the construction of chromatographic columns, particularly capillary and SCOT columns, for reasons of its low catalytic activity toward unstable samples such as steroid derivatives, polar aroma-generating consitutents and certain drug metabolities. Additional advantages of glass columns include the relative ease of the preparation of the tubing and the often greater reproducibility afforded the preparation of high-efficiency chromatographic columns.
In order to obtain columns of high separating power, a regular homogeneous film of the stationary phase must be deposited on the entire surface, e.g., along the entire length of the inner surface of a capillary tube. In general, this is difficult to accomplish with ordinary glass surfaces due to their high surface energies and, consequently, the large contact angles exhibited by most organic liquids. Surface treatment procedures such as carbonization or corrosion with both aqueous and gaseous etching media have been suggested to decrease the values of contact angles. However, in order to achieve homogeneous and stable films of different stationary phases, the chemical capatibility of glass surface and the stationary liquid is an important additional factor. In the case of nonpolar stationary liquids, such as hydrocarbons and certain methylsilicone fluids or gums, this condition is met after the reaction of glass surface silanol groups with common silylation agents such as hexamethyldisilazane and trimethylchlorosilane [M. Novotny and K. Tesarik, Chromatographia 1, 332 (1968)]. Stationary phases of different polarity are, however, needed in a number of practical analytical problems.
In U.S. Pat. No. 3,515,923 there is described the preparation of glass column active surfaces by utilization of hydrolytic polymeric products of di- and trihalogenated silanes, di- and trialkoxyorganosilanes and di- and triacetoryorganosilanes as direct separation media (also called chemically-bonded stationary phases) without further chemical modification and wetting with a partitioning liquid.